Tenter clip



March 24, 1959 P. T. KAEsTNER TENTER CLIP Filed July 30, 1954 INVENTOR PAUL T. KAESTNER ATTORNEY United States Patent TENTER CLIP Paul T. Kaestner, New Canaan, Conn., assignor to Olin 1V Ia thieson Chemical Corporation, a corporation of Vir- Application July 30, 1954, Serial No. 446,886

1 Claim. (Cl. 2662) This invention relates to a clip and more particularly to an improved tenter clip especially adaptable for lateral stretching of plastic Webs by automatic machines.

The art of stretching web material by automatic tentering machines has long been known and used. The lateral stretching operation of such machines involves a gripping of the web at its edges by a series of tenter clips mounted upon endless chains on either side of a tenter frame and then stretching by said chains by the use of an adjustable divergent path of travel for said chains from the center line of the web.

Recent advances in the organic plastic web field have revealed that such webs are improved by physical treatments thereof, especially that of stretching. It has been found that the automatic tentering machines heretofore known are especially adaptable for such stretching treatment provided that certain modifications are made therein to render them operable for plastic applications. One modification that must be made involves the use of a tenter clip which will hold tight against the low-coefficients of friction of some of the plastic web materials and at the same time rely on pure clamping action rather than means which puncture or deform localized portions of the surface to produce their gripping actions.

An object of this invention is an improved tenter clip which has a large gripping area. Another object of this invention is an improved tenter clip whose gripping action avoids shearing the Web. A further object of this invention is an improved tenter clip in which accidental releasing of the web is substantially eliminated. A still further object of this invention is an improved tenter clip which has features which make it particularly adaptable to stretching plastic webs. Other objects will become apparent to those skilled in the art upon reading the following detailed disclosure.

In accordance with this invention the foregoing objects as well as others are accomplished generally speaking by providing a tenter clip with matching jaw members having curved surfaces adapted to engage the web so that the line of clamping force forms an acute angle with the perpendicular of the force exerted by the web in its extended position. More particularly, the improved tenter clip of this invention in its preferred embodiment, comprises a lower jaw member and a pivoting upper jaw member which engage so that the line of clamping force is at an angle very acute to the perpendicular of the transverse force exerted by the web. Thus, as the transverse forces increase, the gripping or wedging action also increases because frictional forces between the clip and the web become greater. And due to the fact that the matching jaw members have engaging surfaces, which are shaped to engage a large surface of the web, shearing of the web is prevented. A clip which is particularly adaptable for handling plastic Webs, therefore, results.

This invention can be more aptly described by reference to the accompanying drawings in which:

Figure l discloses a cross sectional side view of one embodiment of the improved tenter clip of this invention,

Figure 2 discloses a pictorial view of the upper pivoting jaw member of the embodiment of the improved tenter clip shown in Figure 1,

Figure 3 discloses a cross sectional side view of another embodiment of engaging surfaces that may be used in this invention.

In Figure 1 there is shown tenter clip frame 1 upon which a lower jaw member 2 and pivoting upper jaw member 3 pivoted at 4 is attached. The frame is shaped at 5 in the form of a link member for attaching it to a continuous chain. In use the clip shown is part of a continuous chain which is comprised of roller chain links connecting a series of tenter clips at 5 for gripping the web of the material being processed. The tenter clip shown in Figure 1 rides upon rails 6 and 7 of the tentering machinery. The lower jaw member 2 of the tenter clip has been faced with a concave surfaced anvil 8. The upper jaw member 3 of the tenter clip has its engaging lip faced with a convex surface whose surface fits into the concave surface of the anvil of the lower jaw member, in this instance being a partially rotatable cylinder 9 which can partially rotate about the lip of the pivoting e a cam contained in the tentering machine.

In Figure 2 there is shown an upper jaw of the tenter clip, the embodiment of which is shown in Figure 1. This upper jaw member 3 consists of a cylindrical engaging lip 9, and an upper extending arm 10. It also contains a joint housing 11 for the purpose of being pivotable when mounted upon the tenter clip frame. The engaging lip 9, as shown, consists of a partially rotatable cylinder, rotatable at joints 16.

In Figure 3 there is shown another embodiment of the engaging lip portion of the tenter clip of this invention. In this case the lower jaw consists of an engaging lip having an anvil 12 whose surface is convex. The upper jaw member 3 has an engaging surface 13 whose surface is concave, such that the convex surface of the lower jaw member will fit into the concave surface of the upper jaw member and thus effect a large gripping surface.

In operation, the tenter clip shown in Figure 1 is mounted through link member at 5 with other tenter clips of similar design so that a continuous chain of clips will be formed. Two such chains are mounted to travel longitudinally at each edge of the Web W. As the web first enters the tentering machine the web is caused to pass between the upper and the lower jaw members of the tenter. This is accomplished by maintaining the pivoting upper jaw member in an open position by the use of a cam which compresses against the extending arm 10 of the upper jaw member. As the web enters the space between the upper jaw member and the lower jaw member, the pivoting upper jaw member is released and engages the web by force of gravity. To assist in such initial engagement, one might, if desired, add a weight to the pivoting jaw member at a point which adds to the force of gravity. An example of such weight is shown in Figure l and labeled 17. A slight gripping action begins.

As the web exerts a pulling force, the frictional force between the web and the contacting surfaces increases thus causing a greater holding or gripping force. This follows from the fact that the holding or gripping forces are equal to the vertical forces clamping the material multiplied by the coeificient of friction of the web against the clip anvil and jaw. The vertical forces clamping the material are first generated by the force of gravity upon the upper pivoting member of the jaw members own weight or of an added weight attached thereto. This acts to start the gripping action. Subsequently the pull of the web causes the upper jaw member to, increasingly wedge against the lower jaw member as it increases. Hence, for a complete gripping or wedging action the line of force generated by the jaw member is actually at an acute angle to the perpendicular of the forces generated by the web being stretched (pulling forces).

Upon reaching the end' of the path of the tentering machine, the pivoting upper jaw member of the tenter clip is released and the web leaves the area between the jaw members of the tentering clip. The clip is then returned to again grip and stretch other portions of the moving web of material.

It is to be noted that by constructing the engaging lips as shown in the drawings, there is effected a clip which not only has an increasing gripping action upon the web as the pulling forces increase, but also cannot be sprung beyond dead center and cannot he accidentally released during the stretching operation. It is also to be noted that to provide a large gripping contact the upper jaw member and the lower jaw member have engaging edges which consist of curved surfaces, preferably one is convex while the other is concave and so permitted to engage each other that the convex shape of one matches the concave shape of the other.

A further feature of this invention is that of the construction of the lip portion of the upper jaw member. It is preferably such that it permits the use of a pivoted or rotatable jaw member, thus eliminating any chance for shear or for scufiing the web as it becomes engaged. Obviously any other curved surface may be used for the engaging surface of the two jaw members.

In use, the clip of this invention has been found to be particularly advantageous for stretching plastic webs such as polyethylene, polyamide, etc. films. Other web materials such as woven fabric, rubber sheeting, etc. might also be advantageously stretched by said clips.

It is to be noted that the particular design of the clip framework shown in the drawings is of no moment. It is the manner of effecting the increased gripping action coupled with the use of engaging surfaces which prevent shearing of the web that is of the essence. In modifying the framework one particular addition to the clip that 4 suggests itself and which is considered obvious to one skilled in the art is that of adding to the clip of Figure 1 a web-engagement control mechanism such as the roller used in the clip shown in the drawing of U.S. 616,390. Other additions obviously are also possible.

While a detailed description of this invention has been provided, it is realized that those skilled in the art may make modifications in and adaptations of the tenter clip disclosed herein. It is, therefore, to be specifically understood that such obvious modifications are to be considered within the spirit and scope of this invention.

The invention having thus been described, what is desired to be secured by Letters Patent is as follows:

A tenter clip including a frame comprising a fixed lower jaw member and a relatively movable upper jaw member, said movable jaw member being pivotal to an open position through a predetermined are bounded by the clip frame and said fixed member, said upper member having a length greater than the gap between the jaws when in the open position and operable upon closing to engage a web disposed between the jaws effective to apply a clamping force to the sheet along a line which forms an acute angle with a line normal to the web, said fixed jaw member having a concave engaging surface and the pivoting jaw member having a mating convex surface, said pivoting jaw member being further characterized by being formed with a movable cylinder rotatable through a predetermined arc.

References Cited in the file of this patent UNITED STATES PATENTS 145,762 Spooner Dec. 23, 1873 860,993 Riley July 23, 1907 1,141,081 Whitley May 25, 1915 1,517,225 Whitley Nov. 25, 1924 1,974,859 Bowden et a1. Sept. 25, 1934 1,982,683 McCann Dec. 4, 1934 FOREIGN PATENTS 5,316 Germany July 30, 1878 135,128 Germany Dec. 13, 1901 

